Implantable medical devices (IMDs) are devices designed to be implanted into a patient. Some examples of these devices include implantable cardiac rhythm management (CRM) devices such as implantable pacemakers, implantable cardioverter defibrillators (ICDs), implantable cardiac resynchronization devices, or devices that include a combination of such capabilities. The devices can be used to treat patients using electrical or other therapy or to aid a physician or caregiver in patient diagnosis such as through internal monitoring of a patient's condition. The devices can include one or more electrodes in communication with one or more sense amplifiers to monitor electrical heart activity within a patient, and often include one or more sensors to monitor one or more other physiological patient parameters. Other examples of implantable medical devices include implantable diagnostic devices, implantable drug delivery systems, or implantable devices with neural stimulation capability, some of which can also be CRM devices.
Additionally, some CRM devices detect events by monitoring electrical heart activity signals, such as heart chamber expansions or contractions. By monitoring cardiac signals indicative of expansions or contractions, IMDs can detect tachyarrhythmia. Tachyarrhythmia includes abnormally rapid heart rate, such as ventricular tachyarrhythmia (VT), supraventricular tachyarrhythmia (SVT), and sinus tachyarrhythmia (ST). Tachyarrhythmia also includes rapid and irregular heart rate, or fibrillation, such as ventricular fibrillation (VF).
Some CRM devices are able to provide therapy for tachyarrhythmia, such as anti-tachyarrhythmia pacing (ATP) or high energy shock therapy. A therapy approach for a VT can include providing ATP to attempt to terminate the tachyarrhythmia. If ATP fails to terminate the tachyarrhythmia after an appropriate amount of time, then shock therapy (e.g., cardioversion or defibrillation) can be introduced, such as via a CRM device.